Ultra precision positioning servo system places severe constraints on the amount of heat can be produced by actuator (motor), and its trust control accuracy. FIG. 1 shows the application of linear motor in ultra precision positioning servo system. On the basic frame 10, there are two X-axis linear motors 12 and two y-axis linear motors 13 to drive and locate the load 11 in a desirable position. Excessive motor temperature rise not only affect its reliability, but also impact on the positioning accuracy as well due to the increase in motor's thermal stress. Besides, ultra-precision positioning servo system is using a laser displacement sensor for position measurement, therefore, the temperature rise in the motor's surface will result in ambient temperature changes and affecting the measurement accuracy of the sensor, thus unable to achieve positioning accuracy.
The coreless motor possess of several advantages in terms of minor armature reaction, no cogging force, and great linear relationship between trust and current, however, the loss caused by its high current density become the major obstacle of its development.